Members of the Tree of Life synagogue in Pittsburgh were gathered to celebrate a baby naming ceremony Saturday morning when a heavily armed gunman opened fire in what’s believed to be the deadliest attack on the Jewish community in U.S. history.

Authorities and court documents have offered a horrific account of how Robert Bowers, 46, gunned down 11 people and wounded six others, including four police officers, in the largely Jewish area of Squirrel Hill near the outskirts of Pittsburgh.

Police say that Bowers pulled up to the synagogue in a teal Hyundai and entered the front door around 9:45 a.m. Shortly after, he burst into a crowded service and fired dozens of rounds, alternating between a AR-15 semi-automatic rifle and three Glock .357 handguns.

A 90-year-old survivor of the shooting, E. Joseph Charny, told the Washington Post that congregants had their heads bowed when the gunshots rang out.

At first, he thought it was a large coat rack falling over.

“I looked up and there were all these dead bodies,” Charny told the Post.“I don’t need to tell you how terrible this has all been.”

Tree of Life Rabbi Jeffrey Myers said there were roughly 12 in the sanctuary at the time of the shooting.

“I helped pull out the people that I could from the front. But, alas, I had eight people in the back. One fortunately survived,” Myers said at a vigil of at least 2,000 gathered at Soldiers and Sailors Memorial Hall Sunday night. “I’m a survivor. I’m a mourner.”

Rabbi Jeffrey Myers of Tree of Life/Or L’Simcha Congregation hugs Rabbi Cheryl Klein of Dor Hadash Congregation on the stage in Soldiers & Sailors Memorial Hall & Museum during a community gathering held in the aftermath of a deadly shooting at the Tree of Life Synagogue in Pittsburgh, Sunday, Oct. 28, 2018.

AP Photo/Matt Rourke

Officials said that as Bowers attempted to leave the synagogue, he exchanged gunfire with police, injuring two officers, before retreating inside the building.

Audio of communications between a 911 dispatcher and police offered a harrowing account as responding officers including a SWAT team were pinned down by automatic gunfire.

“Hold the perimeter, we’re under fire,” an unidentified officer says. “We’re under fire. He’s got an automatic weapon, he’s firing at us from the synagogue.”

Officers chased Bowers up to the third floor of the building where he opened fire again, wounding two SWAT team members in the process. Bowers was eventually subdued after the rampage and is being treated at a local hospital for multiple gunshot wounds.

While he was being treated for his injuries by an officer, Bowers said that “he wanted all Jews to die and also that they (Jews) were committing genocide to his people,” according to court records.

Who are the victims?

Among the victims were professors, dentists, doctors and accountants, including one academic who grew up in Toronto.

A statement from Rabbi Yael Splansky on Facebook says Joyce Fienberg, 75, grew up in the Holy Blossom Temple in Toronto and was married at the temple.

Fienberg and her late husband, Stephen, were well known professors according to those who knew the couple.

The 75-year-old had retired in 2008 after spending most of her career at the University of Pittsburgh’s Learning Research and Development Center, where she studied how people learn from visiting museums.

Dr. Gaea Leinhardt, who was Feinberg’s research partner for decades, said she is devastated by the murder of her colleague and friend.

“Joyce was a magnificent, generous, caring and profoundly thoughtful human being,” she said.

Two of the victims, Cecil Rosenthal, 59, and his younger brother David Rosenthal, 54, were intellectually disabled and lived together near the synagogue where they were killed.

“Cecil’s laugh was infectious. David was so kind and had such a gentle spirit. Together, they looked out for one another. They were inseparable,” said Chris Schopf, vice-president of residential supports for ACHIEVA, which helped the brothers live independently. “Most of all, they were kind, good people with a strong faith and respect for everyone around.”

WATCH: Husband and wife among the victims of Pittsburgh synagogue shooting

Mayor Bill Peduto called it the “darkest day of Pittsburgh’s history.”

“To the victims’ families, to the victims’ friends, we’re here as a community of one for you,” Peduto said. “We will be here to help you through this horrific episode. We’ll get through this darkest day of Pittsburgh’s history by working together.”

Vigils were planned in Pittsburgh, Washington and in communities across Canada. The Pittsburgh Steelers and Cleveland Browns observed a moment of silence at Heinz Field on Sunday along with teams across the NFL.

Who was the shooter?

Robert Bowers, the suspect in the Pittsburgh synagogue shooting.

(NBC)

Little is known about Bowers, who had no apparent criminal record, but social media accounts linked to the alleged gunman showed a neo-Nazi who hated Jews and was angry with Donald Trump for not being anti-Semitic enough.

“I can’t sit by and watch my people get slaughtered,” Bowers wrote on Gab, a social media site favoured by the far right, the morning of the shooting. “Screw your optics, I’m going in.”

Under the bio on the social media account is the phrase “jews are the children of satan.” Authorities believe Bowers acted alone.

He was also charged with several counts of obstructing the free exercise of religious beliefs resulting in death — a federal hate crime — and using a firearm to commit murder.

U.S. Attorney General Jeff Sessions said the charges “could lead to the death penalty.”

Jonathan Perlman, a rabbi who is credited with shielding congregants behind a door during the shooting, spoke at a vigil in Pittsburgh Sunday night about losing loving members of the community who “would give you the shirt off their back.”

“What happened yesterday will not break us. We will continue to thrive and sing and worship and learn together,” Perlman said. “We will not be ruined by this event.”